1. Field of the invention:
The present invention relates to a drainage valve for installation into a water draining conduit. In accordance with the invention, this valve comprises a flexible flap formed with an edge taper to improve water imperviousness.
2. Brief description of the prior art;
U.S. Pat. No. 4,621,945 granted to Schafer et al. on Nov. 11, 1986, illustrates and describes a drainage valve of the above type for installation into an underground water draining conduit. The valve of Schafer et al. comprises a perforated plate on the upstream surface of which is applied a flexible flap. The upper -portion of the flap is attached to the upper portion of the perforated plate through screw and nut assemblies. The lower portion of the flap can be lifted by means of a cord extending into a riser pipe and fixed to the lower flap portion through a bracket. A block element attachable to a pole member is also secured to the upper portions of the flap and plate through the above mentioned screw and nut assemblies to enable installation of the valve into the underground draining conduit from the surface of the ground through the riser pipe.
The drainage valve of Schafer et al. presents the following drawbacks:
the flap is of even thickness over its entire surface; this results in a lack of imperviousness between the plate and flap as the pressure applied on the flap as water upstream of the valve is not sufficient to produce a tight joint by forcing the periphery of the flap on the upstream surface of the perforated plate;
the 0-ring placed between the plate and an inner flange of the underground water draining conduit can cause leakage of water through the valve;
the bracket fixed to the lower portion of the flap requires special cutting out of the plate which often causes water leakage through the valve; and
the block element is in the form of a parallelepiped and comprises exposed acute edges which can cause obstruction upon lifting of the lower portion of the flap through the cord attached to the bracket.